Electron tube



S. R. JEPSON ELECTRON TUBE May 31, 1960 Filed Jan. 18, 1957 56 INVENTOR.

StanIQY R Jcpson BY 7 'I v f ATTORNEY United States Patent ELECTRQN TUBEStanley R. Jepson, Campbell, Calif., assignor to Eitel- McCullough,Inc., San Bruno, Califi, a corporation of California Filed Jan. 18,1957, Ser. No. 635,004

Claims. (Cl. 313-256) This invention relates to electron tubes andparticularly to electron tubes having electrode terminals in the form ofcoaxial conductive rings insulated from each other by ceramic.

At the higher frequencies (e.g. UHF and higher) it is desirable to useco-axial lines and resonant cavity circuits, with correspondingmodifications in tube design to enable electrical connection to theelectrodes thereof through coaxial terminals. For example, a tubedesigned for use in such high frequency circuits may comprise aplurality of ring-like electrode terminals arranged in co-axial array.

However, the fabrication of a tube having co-axial electrode terminalsis not simple. In the first place, it is necessary that the variousterminals be maintained in substantially perfect concentricity thusrequiring a mechanically strong structure. Furthermore, difficulty hasbeen experienced in selecting a material for use as an insulator betweenco-axial terminals. This is due to the fact that the insulator must beinterposed between the terminal rings where it cannot be cooled, theterminal rings eifectively forming ovens containing such insulator. Thusinsulators made of glass, for example, are heated to a comparativelyhigh temperature during the operation of the tube and tend to break downboth mechanically and electrically.

These problems may be diminished through the use of ceramic as theinsulator between the terminal rings. Ceramic possesses greatermechanical strength than glass. Furthermore, ceramic may be heated to ahigher temperature without impairing its mechanical or electricalcharacteristics. However, ceramic structures have been more expensive tofabricate. This is due to the fact that the ceramic pants are rigid andare not subject to being molded or otherwise formed during thefabrication of the tube, as is glass. Instead the ceramic parts areaccurately formed within very close tolerances prior to being assembledinto the tube and the hermetic seals between the ceramic parts and metalparts of the tube are made after such assembly. In addition, thedifferential in thermal coefficient of expansion between the metals andceramics has complicated the design of electron tubes utilizing ceramicssince it tends to make seals between such metals and ceramicsunreliable.

It is an object of this invention to provide an improved electron tubeutilizing ceramic which issimple and inexpensive to fabricate.

It is a further object of the invention to provide an improved electrontube possessing increased mechanical strength throughout a greatertemperature range. 7 It is yet another object of this invention toprovide an electron tube having an improved arrangement of coaxialelectrode terminals insulated from each other by ceramic.

Briefly an electron tube according to one embodiment of this inventioncomprises a metallic electrode terminal member having a flat surface, aceramic member mounted on a portion of the flat surface ofthe metallicterminal 2,939,032 Patented May 31, 1960 ICC member, and a ceramic ringsurrounding the ceramic member and having one end hermetically sealed tothe flat surface of the metallic terminal member. The ceramic member hasa metallic coating on the exterior surface thereof and an electrode ismounted on the ceramic member opposite from the metallic member, themetallic coating electrically connecting the electrode and the metallicterminal member. The ceramic ring may have a metallic ring hermeticallysealed to the outer surface of the end thereof opposite from themetallic member, the metallic ring being insulated from the metallicmember by the ceramic ring.

.The invention possesses other objects and features of advantage, someof which, with the foregoing, will be set forth in the followingdescription of the invention. It is to be understood that the inventionis not limited to the disclosed species, as variant embodiments thereofare contemplated and may be adopted within the scope of the claims.

The invention will be more completely described hereinafter withreference to the attached single sheet of drawing wherein the figure isa view partially in elevation and partially in cross-section of anelectron tube embodying this invention.

Referring to the figure, a tube embodying this invention may be any typeof tube having co-axial electrode terminals as illustrated. It should beunderstood that, although the tube 10 chosen for illustration is atetrode having cylindrical electrodes, this invention is not limited touse in tetrodes or in tubes having cylindrical electrodes, but would beequally applicable to a mode having planar electrodes, for example, asWell as to tubes employing velocity modulation such as klystrons ortraveling wave tubes.

As shown in the figure, an indirectly heated cathode 12 is located atthe' center of the tube 10. A cylindrical control electrode 14 surroundsthe cathode 12 and a cylindrical screen electrode 16 surrounds thecontrol elec trode 14. An inverted cup-shaped anode 18 surrounds thescreen electrode 16 and forms a part of the tube envelope. The open endof the anode 18 is provided with an outwardly extending flange 20 towhich one end of an insulating ring 22 (which may be glass, for example)is hermetically sealed. A metallic terminal ring 24 is hermeticallysealed to the opposite end of the insulating ring 22 from the anode 18.A disk 28 having a central aperture and made of insulating material suchas glass is hermetically sealed within the terminal ring 24 by means ofa sealing ring 26. The screen electrode 16 is supported on andelectrically connected to such terminal ring 24 and sealing ring 26 bymeans of hollow metallic skirts 30 and 32. A metallic support cylinder34 is hermetically sealed through the central aperture in the insulatingdisk 28. The control electrode 14 is mounted on and electricallyconnected to the inwardly extending end of the support cylinder 34 by ahollow metallic skirt 35, the other end of the support cylinder 34serving as an electrical terminal for the control electrode 14. Thecathode-heater assembly 36 extends through the control electrode supportcylinder 34 and within the control electrode 14 and is hermeticallysealed to the control electrode support cylinder 34 by means of asealing ring 38, thus completing the vacuum tight envelope of the tube10. The envelope of the tube 10 may be evacuated through an exhausttribulation 39 provided on the anode 18, for example, which may besealed as shown when such evacuation is complete.

The cathode 12 is cup-shaped, the open end thereof being supported onone end of a heat dam cylinder 40 made of thin metal foil. The electronemissive portion of the cathode comprises a coating of therm'ionicallyemissive material on the exterior sidewall 42 of the cupshaped cathode12. A filamentary heater 44 is mounted within the cup-shaped cathode 12.

-'According to this embodiment of the invention, the lower end of theheat dam cylinder 40 is brazed or otherwise attached to areinforcingring 46. The reinforcing ring is provided with a flange 48extending inwardly thereof.

One end of a first ceramic ring 50 is brazed or otherwise rigidlyattached to the lower surface of the flange 48. An annular metallicmember '52 is hermetically sealed as by brazing to the other end of thefirst ceramic ring 50 and extends outwardly from such ceramic ring 50.

The exterior sidewall of the first ceramic ring 50 is provided with ametallic coating 54 which electrically connects the reinforcing ring 46,and thus the cathode 12, to the annular metallic member 52. The annularmetallic member 52 is provided with a downwardly extending cylindricalportion 56 to serve as an electrical terminal for the cathode 12.

A second ceramic ring 58 surrounds the first ceramic ring 50 and is inco-axial relationship therewith. One end of the second ceramic ring 58is hermetically sealed as by brazing to the portion of the annularmetallic member 52 which extends outwardly from the first ceramic ring50.

The metallic sealing ring 38 is hermetically sealed to the opposite endof the second ceramic ring 58 from the annular metallic member '52, thesecond ceramic ring 58 insulating the sealing ring 38 from thecathode-heater assembly.

The'filamentary heater 44 is supported within the cupshaped cathode 12by means of a center support rod 60 extending co-axially within thecathode-heater assembly 36. The center support rod 60 is supported onthe inner surface of the first ceramic ring 50 by means of a pluralityof support rings 62. The support rings 62 are positioned along andbrazed to the support rod 60 and extend between the inner surface of thefirst ceramic ring 50 and the support rod 60. At least one of thesupport rings 62 is hermetically sealed about its outer periphery to theinner surface of the first ceramic ring 50. It will be seen that thesupport rod is thus supported by the support rings 62 at a plurality ofpoints spaced along its axis, thereby insuring the co-axial alignment ofthe support rod 60 with the cathode-heater assembly 36 and the rigidmaintenance of such alignment.

One end of the filamentary heater is attached to the inwardly extendingend of the center support rod 60, the heater 44 spiraling downwardlyabout the end portion of the support rod 60. The other end of the heater44 is electrically connected to the cathode 12 by means of a supportpost 64 brazed or otherwise rigidly attached to the upper surface of theflange 48 on the reinforcing ring 46 and extending upwardly within thecathode 12. Thus, the lower end of the center support rod 60 serves asone terminal for the heater 44, the other terminal for the heater 44being the cathode terminal 56.

As shown in the figure a pair of insulating disks 66 may be providedwithin the cathode 12 to act as heat shields and to prevent excessivevibration of the heater 44. The disks 66 are provided with aperturesthrough which the center support rod 60 and the support post 64 pass.The disks are mounted on the center support rod 66 and support post 64by means of wires 68 which pass through other apertures in the disks andare brazed at both ends to rod 60 or post 64. The outer peripheries ofthe disks 66 are in close-spaced relation to the inner surface of theheat dam cylinder 40 and tend to prevent excessive vibration of the rod60, post 64 and heater 44.

In the fabrication of the cathode-heater assembly according to thisembodiment of the invention the first step is to metalize the properportions of the surfaces of the ceramic rings 50 and 58. Such metalizingmay be accomplished, for example, by painting such surface por tions ofthe ceramic rings 50 and 58 with a paint comprising metallic particlessuspended in a volatile binder. For example, a mixture of molybdenum,manganese, and titanium powders suspended in a nitrocellulose binder maybe used. The ceramic rings 50 and 58 are then subjected to heattreatment to volatilize the binder and sinter the metallic powders tothe desired areas thereof.

According to this invention, the entire outer surface including theends, and a small strip about an inner circumference spaced from suchends of the first ceramic ring 50 are provided with metallic coatings asdescribed above. Similarly one of the ends and a portion of the outersurface at the other end of the second ceramic ring 5 8 are providedwith metallic coatings. The thickness of the metallic coating 54 on theouter surface and ends of the first ceramic ring 56 has been exaggeratedin the figure in order to clearly show the electrical connection betweenthe annular metallic member 52 and the reinforcing ring 46. In actualitythe metallic coating is too thin to be shown in cross-section andnoretlort has been made to show the inner metallic coating on the firstceramic ring 50 or the metallic coatings on the second ceramic ring 58which serve solely as part of the hermetic seals made to the ceramicrings 50 and 58.

The second ceramic ring 58 is then forced into the sealing ring 38, thesealing ring '38 having an end portion 70 of slightly smaller internaldiameter than the external diameter of the ceramic ring 58, such thatthe end portion of the ceramic ring 58 having the metallic coating onthe outer surface thereof is placed under compression. Thus, when ahermetic seal is later made between the ceramic ring 58 and the sealingring 38, the strain in the rings 38 and 58 will tend to compensate forthe differential in thermal expansion thereof. Furthermore, thetolerance in dimensions of the parts will tend to be less strict due tothe press fit therebetween.

The support rings 62 are then brazed to the center support rod 60,preferably in the orientation shown. Similarly, the annular metallicmember 52 is brazed to one end of the cathode terminal cylinder 56 inco-axial relation thereto, as shown. It should be understood that themetal-to-metal brazes described above are gas tight and that they have ahigher melting temperature than the metal-to-ceramic brazes to bedescribed hereinafter.

The various parts are then placed in a brazing jig (not shown) made ofcarbon or other material which is not wet by the metal-to-ceramicbrazing material and which may comprise a member provided with aplurality of concentric circular grooves and a central circular recesseach of a diameter corresponding to the part to be positioned therebyand of selected depth. The cathode terminal member 56 and attachedannular metallic member 52 are placed in the jig such that the lower endof the terminal member is received in and aligned by the circular grooveadjacent the central recess. Similarly the center support rod 60 isplaced in the jig suchthat it is supported in a vertical position and inco-axial alignment with the cathode terminal 56 by the engagement of thelower end thereof with the central recess in the jig.

A piece of wire (not shown) made of metal-to-ceramic brazing material isthen wrapped around the center support rod to form a ring supportedwithin the channel formed by the lower supporting ring '62 and the nextadjacent supporting ring 62. A flat washer (not shown) made ofmetal-to-ceramic brazing material is placed on the upper surface of theannular metallic member. The above mentioned metal-to-ceramic'brazingmaterial may be any suitable material, but is preferably copper-silvereutectic which has superior flowing properties when molten.

The first ceramic ring 50 is then positioned about the center supportrod 60 such that the strip of metallic coating on the inner surfacethereof is in alignment with the outer periphery of the lower supportring 62, the ring 50 being supported at its lower end on the annularmetallic' member 52 with the Washer of brazing material therebetween. Itwill be seen that co-axial alignment of the member 52 is obtained byengagement of its inner periphery with the support rings 62. Similarlythe second ceramic ring 58 and the sealing ring 38 into which it ispress fit are positioned in the jig with the lower end of the secondceramic ring 58 in contact with the washer of brazing material on theannular metallic member 52 and the lower end of the sealing ring 38 inengagement with another circular groove in the jig to insure the coaxialarrangement thereof with the other parts of the assembly. A ring orwasher (not shown) of ceramic-tometal brazing material (e.g.copper-silver eutectic) is placed on the upper end of the second ceramicring 58 in position to flow between such ring 58 and the sealing ring 38at brazing temperature. Similarly a fiat Washer (not shown) ofceramic-to-metal brazing material is placed on the upper end of thefirst ceramic ring 50. The reinforcing ring 46 is then placed on theupper end of the first ceramic ring 50 with the lower surface of theinwardly extending flange 48 thereof in contact with the washer ofbrazing material. A cap (not shown) made of the same material as is therest of the jig is placed over "the reinforcing ring 48 and contactsboth the outer surface of the reinforcing ring 46 and the outer surfaceof the first ceramic ring 50 to secure co-axial alignment thereof. Ahole is provided in such cap through which the support post 64 isinserted and by which the support post 64 is held in an upright positionwith the lower end thereof in contact with the upper surface of theinwardly extending flange 48 of the reinforcing ring 46. A drop ofbrazing material, which may be the same as the metal to-ceramic brazingmaterial, is attached to the lower end of the support post 64 to bond itto the reinforcing ring. The cap is also provided with a centrallylocated hole through which the center support rod 60 projects.

The jig with the assembled parts is then placed in an oven and heated tobrazing temperature. The brazing material melts and flows between theparts to be brazed thus accomplishing all of the brazes simultaneously.The assembly is allowed to cool and is then ready for the attachment ofthe insulating disks 66, the heater 44, and the previously assembledcathode 12 and heat dam cylinder 40 in that order. After such attachmentthe completed heater-cathode assembly 36 may be assembled with theremaining portions of the tube, the sealing ring 38 being arc welded atits lower end to the grid support cylinder 34 to provide a hermetic sealtherebetween.

Due to the simplicity of fabrication and to the inexpensive methods madepossible thereby a tube embodying this invention is adapted for highproduction techniques. Furthermore, the mechanical and electricalcharacteristics of a tube embodying this invention represent asubstantial improvement over the prior art and make possible many newapplications thereof particularly when dependability and ruggedness arerequired.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is: i 1. An electron tube having aplurality of electrodes, including a cathode and an anode, said tubecomprising a metallic electrode terminal member having a flat surface, aceramic member mounted on one portion of said flat surface of saidmetallic member, and a ceramic ring surrounding said ceramic member andhaving one end hermetically sealed. to another portion of the same fiatsurface of said metallic member, one of said plurality of electrodesbeing mounted on said ceramic member, and a metallic coating on asurface of said ceramic member electrically connecting said electrode tosaid metallic member.

2. An electron tube comprising a plurality of electrodes, including acathode and an anode contained within anlev'acuated envelope, saidenvelope comprising a meiallic electrode terminal member having twooppositely disposed major surfaces, a ceramic ring, one end of saidceramic ring being hermetically sealed to one of said major surfaces ofsaid metallic member, and a metallic ring hermetically sealed to theopposite end of said ceramic ring from said metallic member, a ceramicmember mounted on said metallic member within said ceramic ring, saidceramic ring and said ceramic member being in nonabutting relationship,and on the same one of said major surfaces of said metallic member andon flat portions of said major surface one of said plurality ofelectrodes being mounted on said ceramic member, and a metallic coatingon a surface of said ceramic member electrically connecting said oneelectrode to said metallic member.

3. An electron tube comprising a plurality of electrodes, including acathode and an anode contained within an evacuated envelope, saidenvelope comprising a metallic electrode terminal member having a flatsurface, a first ceramic ring, one end of said first ceramic ring beinghermetically sealed to a portion of said flat surface of said metallicmember, a second ceramic ring surrounding said first ceramic ring andhaving one end hermetically sealed to another portion of the same flatsurface of said metallic member, and a metal ring hermetically sealed tosaid second ceramic ring at the end thereof opposite from said metallicmember, one of said plurality of electrodes being mounted on said firstceramic ring, and a metallic coating on a surface of said first ceramicring electrically connecting said electrode to said metallic member.

4. An electron tube comprising a plurality of electrodes, including acathode and an anode contained within an evacuated envelope, saidenvelope comprising an annular metallic electrode terminal member havinga flat surface, a first ceramic ring, one end of said first ceramic ringbeing hermetically sealed to a portion of said flat surface of saidannular metallic member, a second ceramic ring surrounding said firstceramic ring and having one end hermetically sealed to another portionof the same fiat surface of said annular metallic member, said ceramicrings being in co-axial relationship to each other, an elongated supportrod extending co-axially within said ceramic rings and said metallicmember, and a metallic ring having its inner periphery hermeticallysealed to said support rod and its outer periphery hermetically sealedto a circumferential portion of the inner surface of said first ceramicring, one of said plurality of electrodes being mounted on said firstceramic ring, and a metallic coating on the outer surface of said firstceramic ring electrically connecting said one electrode and saidmetallic member.

5. An electron tube comprising a plurality of electrodes, including acathode and an anode contained within an evacuated envelope, saidenvelope comprising a hollow cylindrical metallic member having a fiatradially extending surface, a first ceramic ring having one endhermetically sealed to said radially extending surface of said metallicmember, a second ceramic ring surrounding said first ceramic ring inspaced relation thereto and having one end hermetically sealed to thesame radially extending surface of said metallic member, said ceramicrings being in co-axial relationship to each other and to said metallicmember, an elongated metallic rod extending co-axially through saidmetallic member and said ceramic rings, a hermetic seal between said rodand the inner surface of said first ceramic ring, and a metallic ringhermetically sealed to the end portion of said second ceramic ringopposite from said metallic member, said metallic ring being co-axialwith said rod and with said cylindrical metallic member.

6. An electron tube comprising a plurality of electrodes, including acathode and an anode contained Within an evacuated envelope, saidenvelope comprising a hollow cylindrical metallic electrode terminalmember having a fiat radially extending surface, a first ceramic ring,one end of said first ceramic ring being hermetically sealed to aportion of said flat surface of said annular metallic member, a secondceramic ring surrounding said first ceramic ring and having one endhermetically sealed to another portion of the same flat surface of saidannular metallic member, said ceramic rings being in coaxialrelationship to each other, an elongated rod extending co-axiallythrough said ceramic ring and said metallic member, a metallic ringextending radially outward from the outer surface of said rod to theinner surface of said first ceramic ring, said metallic ring beingspaced from the ends of said' rod and said first ceramic ring and beinghermetically sealed to the outer surface of said rod and the innersurface of said first ceramic ring, and a metallic terminal ringhermetically sealed to the end portion of said second ceramic ringopposite from said annular metallic member, a first one of saidplurality of electrodes being mounted on said first ceramic ring, ametallic coating on the outer surface of said first ceramic ringelectrically connecting said first electrode to said cylindricalmetallic terminal member, and a second one of said plurality ofelectrodes mounted on and electrically connected to said metallicterminal ring.

7. An electron tube having a plurality of electrodes, including acathode and an anode, said tube comprising an envelope, said envelopecomprising a hollow cylindrical metallic member having a flat radiallyextending surface, a first ceramic ring having one end hermeticallysealed to said radially extending surface of said metallic member, saidfirst ceramic ring having a metallic coating on the outer surfacethereof electrically connected to said metallic member, a second ceramicring surrounding said first ceramic ring in spaced relation thereto andhaving one end hermetically sealed to the same radially extendingsurface of said metallic member, said ceramic rings being in co-axialrelationship to each other and to said metallic member, an elongatedmetallic rod extending co-axially within said metallic member andthrough said ceramicrings, and a hermetic seal between said rod and theinner surface of said first ceramic ring, and a filament mounted on saidrod, one end of said filament being electrically connected to said rodand the other end of said filament being electrically connected to saidmetallic coating on said first ceramic ring.

'8. An electron tube having a plurality of electrodes, including acathode and an anode, said tube comprising an envelope, said envelopecomprising a first hollow cylindrical metallic member having a flatradially extending surface, a first ceramic ring having one endhermetically sealed to a portion of said radial surface of said metallicmember, said first ceramic ring having a metallic coating on the outersurface thereof electrically connected to said metallic member, a secondceramic ring surrounding said first ceramic ring and having one endhermetically sealed to another portion of the same radially extendingsurface, said rings being in co-axial relationship to each other and tosaid metallic member, an elongated metallic rod extending co-axiallywithin said metallic member and through said ceramic rings, a hermeticseal between said rod and the inner surface of said first ceramic ring,and a metallic ring surrounding said second ceramic ring and a portionof said metallic member, said metallic cylinder having a restrictedportion hermetically sealed to the end portion of said second ceramicmember opposite from said cylindrical metallic member, a filamentmounted on said rod, one end of said filament being electricallyconnected to said rod and the other end of said filament beingelectrically connected to said metallic coating on said first ceramicmember, one of said plurality of electrodes being electrically connectedto said metallic ring whereby said metallic ring, said metallic cylinderand said metallic rod may serve as electrical terminals for said tube.

9. An electron tube comprising a plurality of electrodes including acathode, an anode, and a filamentary heater contained within anevacuated envelope, said envelope comprising an annular metallicelectrodeterminal member having two oppositely disposed major sur faces,a first ceramic ring having a metallic'coating on the'outersur'facethereof, one end of said first ceramic ring being hermetically sealed toone of said major surfaces of said annular metallic member, a secondceramic ring surrounding said first ceramic ring in spaced relationthereto and having one end hermetically sealed to the same one of saidmajor surfaces of said annular metallic member and on the flat portionsof said major surface, said ceramic rings being in co-axial relationshipto each other and to said annular metallic member, an elongated metallicrod Within and in spaced coaxial relation with said first ceramic ringand said annular metallic member, a hermetic seal between said rod andthe inner surface of said first ceramic ring at an area spaced from theends of said rod and said first ceramic ring, and a metallic electrodeterminal ring sealed to the end portion of said second ceramic ringopposite from said annular metallic member, said filamentary heaterbeing mounted on said rod, one end of said heater being electricallyconnected to said rod and the other end of said heater beingelectrically connected to said metallic coating on said first ceramicring, said cathode being mounted on said first ceramic ring andelectrically connected to said metallic coating, said metallic coatingelectrically connecting said heater and said cathode to said annularmetallic member, and another one of said plurality of electrodes beingelectrically connected to said metallic terminal ring.

10. An electron tube comprising a plurality of electrodes including acathode, an anode, a filamentary heater, and a control electrodecontained within an evacuated envelope, said envelope comprising a firsthollow cylindrical metallic member having a flat radially extendingsurface, a first ceramic ring, one end of said first ceramic ring beinghermetically sealed to a portion of said radial surface of said firstmetallic member and said first ceramic ring having a metallic coating onthe outer surface thereof electrically connected to said first metallicmember, a second ceramic ring surrounding said first ceramic ring andhaving one end hermetically sealed to another portion of the same radialsurface of said first metallic member, said ceramic rings being inco-axial relationship to each other and to said first metallic member,an elongated metallic rod extending co? axially Within said firstmetallic member and through said ceramic rings, a hermetic seal betweensaid rod and a circumferential portion of the inner surface of saidfirst ceramic ring, and a second hollow cylindrical metallic membersurrounding said second ring and a portion of said first metallicmember, said second metallic member having a portion of restrictivediameter hermetically sealed to said second ceramic ring at the endthereof opposite from said first metallic member, said filamentaryheater being mounted on said rod, one end of said heater beingelectrically connected to said rod and the other end of said heaterbeing electrically connected to said metallic coating on said firstceramic ring, said cathode being mounted on said first ceramic ring andelectrically connected to said metallic coating thereon, and saidcontrol electrode being mounted on and electrically connected to saidsecond metallic member, whereby said first and second metallic membersand said metallic rod'may serve as electrical terminals for said tube.

References Cited in the file of this patent UNITED STATES PATENTS2,629,066 Eitel et a1 Feb. 17, 1953 2,683,831 Skehan July 13, 19542,719,185 Sorg et :al. Sept. 27, 1955 2,720,608 Wihtol Oct. 11, 19552,722,624 Doolittle Nov. 1, 1955 2,819,421 Ringland et a1. Jan. 7, 1958i ne-dd UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,939,032 May 31, 1960 Stanley Ru Jepson It is hereby certified thaterror appears in theprinted specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6 line 8, after "relationship" strike out the comma; line 10,after "surface" insert a comma.

Signed and sealed this 22nd day of November 1960,

(SEAL) Attest:

KARL I-I. AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner ofPatents

